$\begin{cases} f(1)=-1.8 \\\\ f(n)=f(n-1)\cdot 9 \end{cases}$ Find an explicit formula for $f(n)$. $f(n)=$
Solution: From the recursive formula, we can tell that the first term of the sequence is ${-1.8}$ and the common ratio is ${9}$. This is the explicit formula of the sequence: $f(n)= {-1.8}\cdot {9}^{{\,n-1}}$ Note that this solution strategy results in this formula; however, an equally correct solution can be written in other equivalent forms as well.